The decline in rates of protein biosynthesis is a near universal phenomenon which takes place with age in many eukaryotic organs and tissues. The long term objective is to determine what age-related cellular changes are responsible for the decline in rates of synthesis of secretory proteins in exocrine glands, using the rat parotid gland as a model system. The immediate objective is to determine whether the changes in raters of secretory protein synthesis in rat parotid glands result from the changes in the ability of the acinar cells to produce specific messenger RNA (mRNA). The will be done by mRNA-complementary DNA (cDNA) hybridization techniques to identify and quantitate mRNA specific for alpha-amylase, the major secretory protein of the gland. DH1 strain of E. coli carrying a high copy number plasmid Puc9 with inserted salivary amylase sequence at pst 1 sites is available in this laboratory to generate amylase cDNA probe. The cDNA probe will be used to compare the age-related differences in rates of amylase gene transcription and accumulation of amylase mRNA in glands which have been depleted of stored secretory proteins stimulated discharge. Specific aims of the proposed study are to determine age-related differences in: a. the available amount of amylase mRNA in unstimulated glands. b. the lag time between stimulated secretion and accumulation of amylase mRNA, c. the rate of transcription of the amylase gene, d. the extent of amylase mRNA accumulation, e. the molecular sizes of the accumulating mRNA, f. the translational activity of total and amylase mRNA that accumulates, and g. the rate of synthesis and accumulation of amylase itself in relation to the above mRNA changes.